With the increasing functionality and miniaturization of radio communication devices such as cellular phones in recent years, multi-resonance and miniaturization of antenna units used in such radio communication devices are being pursued.
As such antenna units, for example, there are techniques disclosed in Japanese Unexamined Patent Application Publication No. 2005-101840 (Patent Document 1) and Japanese Unexamined Patent Application Publication No. 2004-312628 (Patent Document 2).
The antenna unit disclosed in Patent Document 1 handles a wide band ranging from 3 GHz to 10 GHz by means of two antennas including first and second antennas, thereby achieving multi-resonance and miniaturization of the unit.
Specifically, the operating frequency of the second antenna is set to substantially twice the operating frequency of the first antenna, and the first and second antennas cover 3 GHz to 5 GHz and 6 GHz to 10 GHz, respectively. With this setting, the operating frequency of one of the antennas becomes the anti-resonant frequency of the other antenna, thereby preventing interference of radio waves.
The antenna unit disclosed in Patent Document 2 is a double-resonance diversity antenna unit that handles 2 GHz and 5 GHz. The antenna unit achieves miniaturization and high performance by use of three antennas.
Specifically, the antenna unit is formed by arranging three antenna elements on a circuit board. The three antenna elements are a dual-band antenna adapted to both 2 GHz and 5 GHz bands, an antenna dedicated to 2 GHz, and an antenna dedicated to 5 GHz. The dual-band antenna and the antenna dedicated to 2 GHz are formed as pattern antennas, and the antenna dedicated to 5 GHz is formed as an inverted-F metal plate antenna.